1. Field of the Invention
The present invention is related to control of switches and more particularly to control of multi-port cross-point switches.
2. Background Information
Multi-port switches, or cross-point switches, are found in increasing numbers in modern communication systems, including electrical and optical equipment found in telephony, data, audio, and video networks that are proliferating on the Internet and in the smaller networks found in buildings, laboratories, and offices.
The need for ever faster, more flexible, adaptable and scalable switches is the norm in the evolving technology.
There are numerous patents relating to cross-point switches, one such being U.S. Pat. No. 5,983,260, to Hauser et al. that issued on Nov. 9, 1999, which patent is hereby incorporated herein by reference. This patent discloses a system level switch designed for cell processing, that is packets or formatted frames, and not raw or generic data. The patent does not describe typical addressing and control schemes and therefore relies on the known organizations described below. This patent is typical of the patents in the field.
Known methods of control of cross-point switches fall generally into two categories. First, as shown in FIG. 1, is to multiplex data with the address and control of the switch. FIG. 2 shows the sharing of time between the control, addressing and the data. That is if, for example, there was a four port switch, each port would have a single line or set of lines that will carry address and control followed by data. In this system, the address and control are received, de-serialized and interpreted. The data is then switched to the designated output port and sent along with control and address information. In such a system there must be a known protocol that allows the address and control to be distinguished from the data, and some means for determining when the data has ended. Such packetizing, formatting techniques or protocols are well known in the art, for example using Ethernet, TCP/IP, FTP, and many others known in the art.
One limitation of the above first type of control is the latency caused by the need to de-serialize the address and control information and then direct the data out through a deserializer/reserializer path. For example, if the two channels are running at different clock rates, the data must be deserialized and then serialized at the different clock rate. Such operations include inherent delays called latency.
Other drawbacks of this form of switching include bottlenecks and/or storage requirements. For example, the packetized crosspoint switch has the limitation that the packet currently being sent must be processed and a decision must be made on whether the output port is available or not. In the case that the output port is not available, the packet cannot be sent and the complete path must await the opening of the output path, and the packet must be stored.
Another known switch control arrangement includes using one programming input path of a cross-point switch to program all the ports. This allows all the ports to be set up so that data will flow as directed. FIG. 3 represents this arrangement.
One limitation of this second type of control arrangement is the need for a separate connection from any of the many I/O boards that may wish to send or received data through the cross-point switch. These types of systems usually need a shared backplane bus where they can address and set-up the cross-point switch. This single programming input path also can become a bottleneck, limiting the speed at which the crosspoint switch can be programmed for one configuration and then reprogrammed later for a different configuration. In comparison, the first type of control is accomplished through the same input/output lines that transmit the data with no need for extra inputs.
There is a need to improve the switch setup and data throughput latencies.